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Old 9th May 2004, 03:00 PM   #1
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Default Repair issue, please advise

Hi all,

I'm hoping someone will be able to tell me what the problem is on this unit or steer me towards a reputable repair tech.

I recently got an Onkyo TS-DX777 receiver as part of a swap recently, and despite the trader's assurance (surprise surprise), it has problems (I know, 'caveat emptor').

The unit will power up and appears to work normally, e.g. the remote brings up all the appropriate options on the display, and the AM/FM tuner locks onto local stations.

However, it doesn't put out any power to the speakers (tried several and checked w/a multimeter).

When turned up to maximum volume, a circuit breaker engages and shuts the unit down.

Any help/advice would be GREATLY appreciated.

- Dave
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Old 9th May 2004, 09:44 PM   #2
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looks like the poweramp is faulty and puts out a DC voltage when the volume is turned up.
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Old 10th May 2004, 02:21 PM   #3
K-amps is offline K-amps  United States
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If DC increases with volume then the power amp may be ok. Because it is amplifying DC and thats what it does.... amplify. In that case the preamp may be faultyor a faulty source.

However if the DC is constant then probably the power amp is faulty.
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Old 10th May 2004, 06:06 PM   #4
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Hi All,

First, thanks for chiming in. I checked the speaker wire terminals with a multimeter and there is no voltage reading at any volume level.

I pulled the cover and checked the fuses for continuity, all are fine (should have done this first, sorry).

On visual inspection nothing looks out of place on the boards (no burn marks, capacitors all look OK, etc.).

One interesting thing I noticed is that when first plugged in and the main power is switched on, the fan moves a teeny bit but does not turn on. Subsequent switching on and off doesn't do anything. Unplugging it, waiting a bit, and then plugging back in and turning on the main makes the fan move again.

-Dave
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Old 10th May 2004, 06:53 PM   #5
K-amps is offline K-amps  United States
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Now I am beginning to suspect the protection circuit may be acting up.

Try read the voltages off the emitter resistors and ensure they are below 50mVdc.

If you get high voltages close to the rail voltages, the outputs are shorted.
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Old 10th May 2004, 07:24 PM   #6
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Ok, there's 4 white twin style resistors about 4mm thick and the size of a postage stamp type BPR55 0.22 Ohm (manufactured by KOA).

Two are on the board with the power capacitors and two are on the daughterboard attached to it.

Are these the guys I should check?

Thanks,

Dave

PS Did I mention you guys are awesome? Ok, there it is.
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Old 10th May 2004, 07:39 PM   #7
K-amps is offline K-amps  United States
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Yup those are the ones.
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Old 10th May 2004, 09:57 PM   #8
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Ok, here's what I found out:

(there's actually 5)

Resistor #1: Measuring from the outer legs to the inner, 45mVDC, outer leg to outer leg, 96mVDC

#2 from outer to outer 1.25, inner to outer .64

#3 0V!

#4 6V outer and inner

#5 Um... Ok, sit down so your *** doesn't come off when you start laughing... I slipped with the probe and shorted out on a bridge wire, which exploded. After removing the power board & fet sink, I repaired the bridge - but didn't spot that a teeeeny bit of solder shorted to another connection, which fried a tiny transistor. Fortunately, the face didn't explode, so I was able to read the numbers and it looks like I can order 20 for $2, so at least now I can blow up another 19 if I'm so inclined...

So... Hopefully you guys won't have given up hope on me when I get that xisitor in so I can continue my "break it REAL GOOD then fix it" home 'lectronics repair course.

Ahhhh $h!t..!
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Old 11th May 2004, 02:01 PM   #9
K-amps is offline K-amps  United States
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Let us know how it goes...
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Old 11th May 2004, 03:11 PM   #10
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Quote:
Originally posted by K-amps
Let us know how it goes...

You asked him to do measurements, which he did. Aren't going to tell him what those measurements indicate? Or you want me to take over?

Jan Didden
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